1. Field of the Invention
The present invention relates in general to the field of monitoring memory circuits used in integrated circuits, and in particular to a method and system for monitoring memory circuits and a corresponding integrated circuit designed with monitoring memory circuits. The present invention also relates to a data processing program and a computer program product for monitoring memory circuits that comprise a multiple of memory cells.
2. Description of the Related Art
Random variations in the characteristics and operating conditions of static random access memory (SRAM) or in dynamic random access memory (DRAM) can result in read and write failure in these devices. In particular, state-of-the-art deep sub-micron very large scale integration (VLSI) technology suffers from a significant amount of silicon aging problems that lead to reliability problems for embedded SRAM or DRAM memory cells. While it is well-known how to test and characterize these memory cells in the lab, it is getting more and more critical to make sure that these memories continue to work correctly in the field under various operating conditions like voltage and temperature. In order to compensate aging effects and to prevent early failure of a device in the field, the legal operating conditions have to be specified in a very conservative manner; however, large safety margins when characterizing the devices reduce the yield. Also, with respect to the voltage, these aging effects result in higher than strictly required voltage requirements, causing even faster aging during the lifetime of the chip.
In the Institute for Electronics and Electrical Engineers (IEEE) paper “Design and Analysis of a Self-Repairing SRAM with On-Chip Monitor and Compensation Circuitry” by Nildadri Narayan Mojumder et al, 26th IEEE VLSI Test Symposium, 2008, Apr. 27, 2008-May 1, 2008, Pages 101-106, on-chip monitors are disclosed which directly sense the global read stability and writability of the cell. However, in this publication the structure of the cells themselves, used as on-chip monitors, is modified to measure circuit parameters, which makes it very difficult to determine the characteristics and/or the specifications and/or the behavior of regular memory cells used in the memory circuit to be monitored.